1. Field of the Invention
The present invention relates to a molding process for producing elastomeric profiles, for example straps, belts, gaskets, etc. and, in particular, for obtaining closed profiles. More specifically, molding is carried out sequentially, the process according to the invention being particularly suitable for obtaining elastomeric profiles with a large circumference, for example profiles having a diameter of at least one meter. The term "molding" is generally interpreted as the combined operations of molding and vulcanization of a preform.
The invention also relates to a portable device or portable "mold" used for manufacturing or finishing profiles, in particular seals, in situ, that is on the actual site where they are to be used. This portable version is of great interest as it eliminates delays for delivery, the storage of ad hoc stock and, in particular, affords the possibility of producing directly or finishing on site a profile having the exact size required for the parts to be assembled. This deciding factor allows maintenance operations directly on site as soon as it is noticed, for example, that a seal or other profile needs to be changed.
For the sake of clarity and simplicity in the specification, the invention will be described hereinafter in relation to seals or gaskets, but it should be understood that it also relates to other types of profiles such as straps, belts and the like which pose the same problem of production and finishing as seals.
2. Description of the Prior Art
The known processes for producing elastomeric gaskets generally involve compression or injection molding or extrusion techniques.
The techniques of molding by compression with a closed circular mold and by injection are not suitable for obtaining large circumference seals. In fact, the mold used defines the profile of the seal and also its diameter in both cases. Consequently, the maximum circumference of the seal is limited by the dimensional capacities of the press receiving the mold and by criteria concerning bulk. Furthermore, for the same seal profile it is necessary to use a different mold for each different diameter.
Large circumference seals are generally obtained by an extrusion process. In a process of this type, molding of the seal takes place dynamically by continuously advancing material through a die to form the shape of the seal. For a given seal profile, a single die is required whatever the diameter of the desired seal.
However, a major drawback of this process resides in the need to abut the two ends of the seals molded in this way, after molding, in order to obtain a closed element. This abutment is generally carried out by hot or cold adhesion which is manifested by a discontinuity in vulcanization and incidentally by an alteration in the intrinsic characteristics of the seal, in particular the tear strength.
Furthermore, the dimensional tolerances of the section of the seal obtained by extrusion are relatively wide, for example of the order of .+-.0.6 mm over a section of 15 mm, and results in a relatively coarse surface, two parameters which have a great influence on the quality of the seal.
A sequential molding process adapted to the production of rubber belts is also known. The preform of these belts are closed and with the molding taking place after this preform has been tensioned between two opposing pulleys of which the spacing is adjustable as a function of the desired length of the belt.
In this process, the length of the elements is necessarily limited by the spacing between the pulleys which cannot be too distant for reasons of bulk. Furthermore, vulcanization of adjoining segments of belt causes edge effects or over-vulcanization, which also leads to irregularities in the characteristics of the finished elements.